Thermoregulation in Malayan sun bears (Helarctos malayanus) and its consequences for in situ conservation

Thermoregulation in Malayan sun bears is not fully understood. Therefore, in this study the effect of meteorological variables on both behavioural and autonomic thermoregulatory mechanisms in sun bears was examined in order to identify temperature thresholds for the activation of various thermoregulatory mechanisms. Infrared thermography was used to non‒invasively determine body surface temperature (T_S) distribution in relation to ambient temperature (T_A) and to determine the thermoneutral zone (TNZ) of sun bears. Thermographic measurements were performed on 10 adult sun bears at T_A between 5 °C and 30 °C in three European zoos. To assess behaviours that contribute to thermoregulation, nine adult sun bears were observed at T_A ranging from 5 °C to 34 °C by instantaneous scan sampling in 60 s intervals for a total of 787 h. Thermographic measurements revealed that the TNZ of sun bears lies between 24 °C and 28 °C and that heat is equally dissipated over the body surface. Behavioural data showed that behaviours related to thermoregulation occurred in advance of energetically costly autonomic mechanisms, and were highly correlated with T_A and solar radiation. While the temperature threshold for the onset of thermoregulatory behaviours below the TNZ lies around 15 °C, which is well below the lower critical temperature (T_LC) assessed by thermography, the onset for behaviours to prevent overheating occurred at 28 °C, which was closer to the estimated upper critical temperature (T_UC) of sun bears. These findings provide useful data on the thermal requirements of sun bears with respect to the species potential to cope with the effects of climate change and deforestation which are occurring in their natural range. Furthermore, these results may have important implications for the care and welfare of bears in captivity and should be taken into consideration, when designing and managing facilities.     

Geographic variation and acclimation effects on thermoregulation behavior in the widespread lizard Liolaemus pictus

Populations at the warm range margins of the species distribution may be at the greatest risks of extinction from global warming unless they can tolerate extreme environmental conditions. Yet, some studies suggest that the thermal behavior of some lizard species is evolutionarily rigid. During two successive years, we compared the thermal biology of two populations of Liolaemus pictus living at the northern (warmer) and one population living at the southern (colder) range limits, thus spanning an 800 km latitudinal distance. Populations at the two range margins belong to two deeply divergent evolutionary clades. We quantified field body temperatures (T_b), laboratory preferred body temperatures (PBT), and used operative temperature data (T_e) to calculate the effectiveness of thermoregulation (E). During one year in all populations, we further exposed half of the lizards to a cold or a hot acclimation treatment to test for plasticity in the thermal behavior. The environment at the southern range limit was characterized by cooler weather and lower T_e. Despite that, females had higher T_b and both males and females had higher PBT in the southernmost population (or clade) than in the northernmost populations. Acclimation to cold conditions led to higher PBT in all populations suggesting that plastic responses to thermal conditions, instead of evolutionary history, may contribute to geographic variation. Lizards regulated moderately well their body temperature (E≈0.7): they avoided warm microhabitats in the northern range but capitalized on warm microhabitats in the southern range. We review literature data to show that Liolaemus species increase their thermoregulation efficiency in thermally challenging environments. Altogether, this indicates that habitats of low thermal quality generally select against thermoconformity in these lizards.     

Latitudinal comparison of the thermal biology in the endemic lizard Liolaemus multimaculatus

Thermoregulation in ectotherms may be modulated by climatic variability across geographic gradients. Environmental temperature varies along latitudinal clines resulting in heterogeneous thermal resource availability, which generally induces ectotherms to use compensatory mechanisms to thermoregulate. Lizards can accommodate to ambient temperature changes through a combination of adaptive evolution and behavioral and physiological plasticity. We studied the thermal ecology of the endangered endemic lizard Liolaemus multimaculatus at six different sites distributed from the northern to southern areas of the distribution (700 km) in the Atlantic dune barriers of Argentina, and even including the borders areas of the distribution range. Environmental temperatures and relative humidity showed a strong contrast between northern and southern limits of the distribution range. The northern localities had operative temperatures (Te) above the range of preferred temperatures (Tset), instead, the southern localities had large proportion of Tes within the Tset. Although these different climatic conditions may constrain the thermal biology of L. multimaculatus, individuals from all localities maintained relatively similar field body temperatures (XTb = 34.07 ± 3.02 °C), suggesting that this parameter is conservative. Thermal preference partially reflected latitudinal temperature gradient, since lizards from the two southernmost localities showed the lowest Tsel and Tset. Thermoregulatory efficiency differed among localities, since E values in the northern localities (E = 0.53–0.69) showed less variability than those of southern localities (E = 0.14–0.67). Although L. multimaculatus employed a strategy of having a conservative Tb and being able to acclimatize the thermal preference to copes with latitudinal changes in the thermal environment, other local factors, such as ecological interactions, may also impose limitations to thermoregulation and this may interfered in the interpretation of results at wider spatial scale.     

Long-Range Correlations in Rectal Temperature Fluctuations of Healthy Infants during Maturation

Background

Control of breathing, heart rate, and body temperature are interdependent in infants, where instabilities in thermoregulation can contribute to apneas or even life-threatening events. Identifying abnormalities in thermoregulation is particularly important in the first 6 months of life, where autonomic regulation undergoes critical development. Fluctuations in body temperature have been shown to be sensitive to maturational stage as well as system failure in critically ill patients. We thus aimed to investigate the existence of fractal-like long-range correlations, indicative of temperature control, in night time rectal temperature (T_rec) patterns in maturing infants.

Methodology/Principal Findings

We measured T_rec fluctuations in infants every 4 weeks from 4 to 20 weeks of age and before and after immunization. Long-range correlations in the temperature series were quantified by the correlation exponent, α using detrended fluctuation analysis. The effects of maturation, room temperature, and immunization on the strength of correlation were investigated. We found that T_rec fluctuations exhibit fractal long-range correlations with a mean (SD) α of 1.51 (0.11), indicating that T_rec is regulated in a highly correlated and hence deterministic manner. A significant increase in α with age from 1.42 (0.07) at 4 weeks to 1.58 (0.04) at 20 weeks reflects a change in long-range correlation behavior with maturation towards a smoother and more deterministic temperature regulation, potentially due to the decrease in surface area to body weight ratio in the maturing infant. α was not associated with mean room temperature or influenced by immunization

Conclusions

This study shows that the quantification of long-range correlations using α derived from detrended fluctuation analysis is an observer-independent tool which can distinguish developmental stages of night time T_rec pattern in young infants, reflective of maturation of the autonomic system. Detrended fluctuation analysis may prove useful for characterizing thermoregulation in premature and other infants at risk for life-threatening events.     

Thermal biology of the southernmost lizards in the world: Liolaemus sarmientoi and Liolaemus magellanicus from Patagonia,Argentina

We determined the efficiency of thermoregulation by the southernmost liolaemids Liolaemus sarmientoi and L. magellanicus from Patagonia, Argentina (51°S), by measuring body (T_b), microenvironmental, and operative temperatures in the field, and preferred body temperatures in the laboratory (T_pref). L. sarmientoi was found to be a poor thermoregulator, whereas L. magellanicus was deemed to be a constrained thermoconformer. Among all known species of Liolaemus, L. sarmientoi and L. magellanicus had the lowest T_b's when tested in the field; however, their T_pref's were similar to other liolaemids. These data suggest that these southernmost liolaemid species have not evolved appropriate thermoregulatory behaviors or made adequate physiological adaptations to face the extreme thermal challenges of their environment.     

Body temperature variation of free-ranging and captive southern brown bandicoots Isoodon obesulus (Marsupialia: Peramelidae)

To investigate patterns of thermoregulation in free-ranging and captive southern brown bandicoots Isoodon obesulus, we measured abdominal body temperature (T_b) of five free-ranging bandicoots over 42 days using implanted data loggers and T_b of three captive bandicoots over 3 months using implanted temperature-sensitive radio transmitters. Bandicoots in the wild had a mean T_b of 36.5±1.0 °C (range 33.4–39.8 °C) and showed a pronounced nychthemeral pattern with two distinct temperature phases. T_b increased at 13:30±2.6 h each day and remained high for 10.65±2.07 h, suggesting a crepuscular and early evening activity pattern. Daily T_b variation of I. obesulus would save considerable energy by reducing daytime thermoregulatory costs in the wild. Captive bandicoots had a similar mean body temperature (36.9±0.2°C) and range (33.0–39.9°C) as free-ranging bandicoots. However, the nychthemeral T_b pattern of captive bandicoots was different from free-ranging bandicoots, with a less pronounced daily cycle and the nocturnal rise in T_b occurring mainly at sunset and the daily decline occurring mainly at dawn.     

Intraspecific alkaloid variation in ladybird eggs and its effects on con- and hetero-specific intraguild predators

Sexual size dimorphism (SSD) is a common phenomenon in animals. In many species females are substantially larger than males. Because body size plays a central role in modulating the body temperature (T _b) of ectotherms, intersexual differences in body size may lead to important intersexual differences in thermoregulation. In addition, because SSD is realized by differences in growth rate and because growth rate is strongly temperature dependent in ectotherms, a conflict between male reproductive behaviour and thermoregulation may affect the expression of SSD. In this study, we investigated the thermal implications of SSD in a reptile exhibiting spectacular female-biased SSD: the northern map turtle (Graptemys geographica). Over three seasons, we collected >150,000 measurements of T _b in free-ranging adult and juvenile northern map turtles using surgically implanted miniature temperature loggers. Northern map turtles exhibited seasonal patterns of thermoregulation typical of reptiles in northern latitudes, but we found that large adult females experienced a lower daily maximum T _b and a narrower daily range of T _b than adult males and small juvenile females. In addition, despite more time spent basking, large adult females were not able to thermoregulate as accurately as small turtles. Our findings strongly suggest that body size limits the ability to thermoregulate accurately in large females. By comparing thermoregulatory patterns between adult males and juvenile females of similar body size, we found no evidence that male reproductive behaviours are an impediment to thermoregulation. We also quantified the thermal significance of basking behaviour. We found, contrary to previous findings, that aerial basking allows northern map turtles to raise their T _b substantially above water temperature, indicating that basking behaviour likely plays an important role in thermoregulation.     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Thermal biology of a colour‐dimorphic snake,Elaphe quadrivirgata,in a montane forest: do melanistic snakes enjoy thermal advantages?

The adaptive significance of colour polymorphisms in animals has received extensive scientific attention. In snakes, a generally accepted hypothesis is that melanistic individuals enjoy thermal advantages compared to normal coloured individuals. Elaphe quadrivirgata on Yakushima Island exhibits a distinct melanistic/striped colour dimorphism. To test this hypothesis, the thermal biology of free‐ranging E. quadrivirgata was investigated using temperature‐sensitive radio transmitters. The thermal quality of habitats was also evaluated using physical models of the snake. In addition, the species' set‐point range (T_set) was estimated using a laboratory experiment. In July, thermal environments appear to be benign because snakes were able to maintain their body temperature (T_b) within T_set from the midday to evening by using average thermal habitats. By contrast, later months of the year were severe in thermoregulation, and snakes had difficulty maintaining their T_b within T_set by using average thermal habitats. There were no significant intermorph differences in thermoregulation indices in any months, whereas slight differences were detected in hourly comparisons. Most of these comparisons indicated active and precise thermoregulation (with respect to T_set) in striped individuals by using thermally favourable but rare microhabitats such as forest gap. Thus, the obtained values do not support the prediction that melanistic individuals are precise thermoregulators. Yet, melanistic individuals do modify their thermoregulation strategy with respect to the available thermal environments in contrast to striped individuals. Together with the fact that body heating is slower in striped individuals than in melanistic individuals under experimental conditions, it is concluded that melanistic individuals have the potential to enjoy thermal advantages but that this might be of no practical use in terms of T_b in the wild because of the greater thermoregulatory efforts of striped individuals, and because melanistic individuals may use forest gap rarely due to conspicuousness to visually orientated predators under the exposed habitat. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 309–322.     

Bat thermoregulation in the heat: Limits to evaporative cooling capacity in three southern African bats

High environmental temperatures pose significant physiological challenges related to energy and water balance for small endotherms. Although there is a growing literature on the effect of high temperatures on birds, comparable data are scarcer for bats. Those data that do exist suggest that roost microsite may predict tolerance of high air temperatures. To examine this possibility further, we quantified the upper limits to heat tolerance and evaporative cooling capacity in three southern African bat species inhabiting the same hot environment but using different roost types (crevice, foliage or cave). We used flow-through respirometry and compared heat tolerance limits (highest air temperature (T_a) tolerated before the onset of severe hyperthermia), body temperature (T_b), evaporative water loss, metabolic rate, and maximum cooling capacity (i.e., evaporative heat loss/metabolic heat production). Heat tolerance limits for the two bats roosting in more exposed sites, Taphozous mauritianus (foliage-roosting) and Eptesicus hottentotus (crevice-roosting), were T_a = ~44 °C and those individuals defended maximum T_b between 41 °C and 43 °C. The heat tolerance limit for the bat roosting in a more buffered site, Rousettus aegyptiacus (cave-roosting), was T_a = ~38 °C with a corresponding T_b of ~38 °C. These interspecific differences, together with a similar trend for higher evaporative cooling efficiency in species occupying warmer roost microsites, add further support to the notion that ecological factors like roost choice may have profound influences on physiological traits related to thermoregulation.     

Dietary fatty acid composition influences tissue lipid profiles and regulation of body temperature in Japanese quail

Many avian species reduce their body temperature (T _b) to conserve energy during periods of inactivity, and we recently characterized how ambient temperature (T _a) and nutritional stress interact with one another to influence physiologically controlled hypothermic responses in Japanese quail (Coturnix japonica). In the present study, we examined how the fatty acid (FA) composition of the diet influences the FA composition of phospholipids in major organs and how these affect controlled hypothermic responses and metabolic rates in fasted birds. For 5 weeks prior to fasting, quail were fed a standard diet and gavaged each morning with 0.7 ml of water (control), or a vegetable oil comprising saturated fatty acids (SFA; coconut oil), or unsaturated fatty acids (UFA; canola oil). Birds were then fasted for 4 days at a T _a of 15°C. We found that, while fasting, both photophase and scotophase T _b decreased significantly more in the SFA treatment group than in the control group; apparently the former down-regulated their T _b set point. This deeper hypothermic response was correlated with changes in the phospholipid composition of the skeletal muscle and liver, which contained significantly more oleic acid (18:1) and less arachidonic acid (20:4), respectively. Our data imply that these two FAs may be associated with thermoregulation.     

Heterothermy in the southern African hedgehog, <Emphasis Type="Italic">Atelerix frontalis</Emphasis>

Most research on mammalian heterothermic responses in southern Africa tends to be laboratory based and biased towards rodents and smaller members of the Afrotheria. In this study, we continuously measured body temperature of southern African hedgehogs (Atelerix frontalis) between April and August 2009 (−10°C < T _a < 43°C), kept under semi-captive conditions. A. frontalis showed a high propensity for torpor with animals spending up to 84% of the measurement period torpid. During this study, A. frontalis displayed the lowest T _b min (ca 1°C) yet recorded in an Afrotropical placental heterotherm. Bout lengths of between 0.7 h (40 min) and 116.3 h (4.8 days) were recorded. Differences in bout length were observed between lighter individuals compared with an individual exhibiting a higher body mass at the onset of winter, with low M _b individuals exhibiting daily torpor whereas a heavier individual exhibited torpor bouts that were indicative of hibernation. Our results suggest that heterothermic responses are an important feature in the energy balance equation of this species and that body mass at the onset of winter may determine the patterns of heterothermy utilised in this species.     

Hibernation and daily torpor in an armadillo, the pichi (Zaedyus pichiy)

Hibernation and daily torpor are physiological strategies to cope with energetic challenges that occur in many mammalian and avian taxa, but no reliable information exists about daily torpor or hibernation for any xenarthran. Our objective was to determine whether the pichi (Zaedyus pichiy), a small armadillo (Xenarthra, Dasypodidae) that inhabits arid and semi-arid habitats in central and southern Argentina and Chile, enters shallow daily torpor or prolonged deep hibernation during winter when environmental temperature and food availability are low. We studied body temperature changes during winter in semi-captive pichis by means of temperature dataloggers implanted subcutaneously. All individuals entered hibernation, characterized by torpor events of 75 ± 20 h during which the subcutaneous temperature (T_sc) decreased to 14.6 ± 2.1 °C. These events were interrupted by periods of euthermia of 44 ± 38 h with a T_sc of 29.1 ± 0.7 °C. After the hibernation season, daily torpor bouts of 4 to 6 h occurred irregularly, with T_sc dropping to as low as 24.5 °C. We conclude that the pichi is a true hibernator and can enter daily torpor outside of the hibernation season.     

Thermal relationships between body temperature and environment conditions set upper distributional limits on oviparous species

We determined the thermal biology of the oviparous Liolaemus boulengeri and the viviparous Liolaemus lineomaculatus populations localised at high and low latitude sites in Patagonia, Argentina. We present data of body temperatures in the field (T_b) and preferred temperature in the laboratory (T_pref), micro-environmental and operative temperatures and the effectiveness of thermoregulation. Liolaemus boulengeri and L. lineomaculatus choose different heat sources for active selection of suitable thermal micro-environments for thermoregulation, and the oviparous L. boulengeri is a more effective thermoregulator (E=0.55) than the viviparous L. lineomaculatus (E=0.43). Even when L. boulengeri is a better thermoregulator and both species show identical timing in the reproductive cycles, there are constraint factors that impose limitations on the southernmost distribution of the oviparous L. boulengeri.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured V˙o₂ during digging and resting at ambient temperature (T_a) below, within, and above thermoneutrality. Digging metabolic rate was lowest at T_a within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (T_b) remained constant at all T_as. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant T_b during digging.     

Energetics of tropical hibernation

In this field study, the energetic properties of tropical hibernation were investigated by measuring oxygen consumption and body temperature of the Malagasy primate Cheirogaleus medius in their natural hibernacula. These lemurs use tree holes with extremely varying insulation capacities as hibernacula. In poorly insulated tree holes, tree hole temperature and body temperature fluctuated strongly each day (between 12.8 and 34.4°C). The metabolic rate under these conditions also showed large daily fluctuations between about 29.0 ml O₂/h and 97.9 ml O₂/h in parallel with changes in body temperature. In well insulated tree holes in very large trees on the other hand, tree hole temperature and body temperature remained relatively constant at about 25°C. Lemurs hibernating in these tree holes showed a more constant metabolic rate at an intermediate level, but hibernation was interrupted by repeated arousals with peak metabolic rates up to 350 ml O₂/h. The occurrence of these spontaneous arousals proved that the ability for thermoregulation persists during hibernation. Arousals were energetically costly, but much less so than in temperate and arctic hibernators. Despite the decisive influence of tree hole properties on the pattern of body temperature and metabolic rate during hibernation, the choice of the hibernaculum does not seem to be of energetic importance. The overall energetic savings by tropical hibernation amounted to about 70% as compared to the active season (31.5 vs. 114.3 kJ/d). Therefore, tropical hibernation in C. medius is an effective, well-regulated adaptive response to survive unfavourable seasons.     

The roles of energetics,water economy,foraging behavior,and geothermal refugia in the distribution of the bat,Macrotus californicus

Summary Energy metabolism, thermoregulation, and water flux ofMacrotus californicus, the most northerly representative of the Phyllostomidae, were studied in the laboratory using standard methods, and energy metabolism and water fluxes were studied in the field using the doubly labelled water method together with a time budget. Daily energy expenditures of free-living bats averaged 22.8 kJ during the winter study period. Approximately 60% of this was allocated to resting metabolism costs while in the primary roosts (22 h/day).Macrotus californicus is unable to use torpor. The thermoneutral zone (TNZ) in this species is narrow (33 to 40 °C) and metabolic rate increased rapidly as ambient temperature decreased below the TNZ. Basal metabolic rate was 1.25 ml O₂/g·h, or 24 J/g·h. Total thermal conductance below the TNZ. was 1.8 mW/g·°C, similar to values measured for other bats. Evaporative water loss showed a hyperbolic increase with increasing ambient temperature, and was approximately 1% of total body mass/h in the TNZ. The success of these bats as year-round residents in deserts in the southwestern United States is probably not due to special physiological adaptations, but to roosting and foraging behavior. They use geothermally-heated winter roost sites (stable year-round temperatures of approximately 29 °C) which minimize energy expenditures, and they have an energetically frugal pattern of foraging that relies on visual prey location. These seem to be the two major factors which have allowedM. californicus to invade the temperate zone.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - T _a ambient temperature - T _b body temperature - T _lc,T _uc lower and upper critical temperature, respectively - TBW total body water - TNZ thermoneutral zone     

Thermoregulation of water foraging wasps (Vespula vulgaris and Polistes dominulus)

A comparison of the thermoregulation of water foraging wasps (Vespula vulgaris, Polistes dominulus) under special consideration of ambient temperature and solar radiation was conducted. The body surface temperature of living and dead wasps was measured by infrared thermography under natural conditions in their environment without disturbing the insects’ behaviour. The body temperature of both of them was positively correlated with T_a and solar radiation. At moderate T_a (22–28 °C) the regression lines revealed mean thorax temperatures (T_th) of 35.5–37.5 °C in Vespula, and of 28.6–33.7 °C in Polistes. At high T_a (30–39 °C) T_th was 37.2–40.6 °C in Vespula and 37.0–40.8 °C in Polistes. The thorax temperature excess (T_th–T_a) increased at moderate T_a by 1.9 °C (Vespula) and 4.4 °C (Polistes) per kW⁻¹ m⁻². At high T_a it increased by 4.0 °C per kW⁻¹ m⁻² in both wasps. A comparison of the living water foraging Vespula and Polistes with dead wasps revealed a great difference in their thermoregulatory behaviour. At moderate T_a (22–28 °C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T_a (30–39 °C) Vespula reduced their active heat production, and Polistes were always ectothermic. Both species exhibited an increasing cooling effort with increasing insolation and ambient temperature.     

Daily and annual patterns of thermoregulation in painted turtles (Chrysemys picta marginata) living in a thermally variable marsh in Northern Michigan

The capacity for an ectothermic reptile to thermoregulate has implications for many components of its life history. Over two years, we studied thermoregulation in a population of Midland painted turtles (Chrysemys picta marginata) in a shallow, thermally variable wetland during summer in Northern Michigan. Mean body temperature (T_b) of free-ranging turtles was greater in 2008 (25.8 °C) than in 2010 (19.7 °C). Laboratory determined thermoregulatory set point (T_set) ranged from 25 °C (T_set-min) to 31 °C (T_set-max) and was lower during the fall (17–26 °C). Deviations of T_b distributions from field measured operative temperatures (T_e) and indices of thermoregulation indicated that C. picta marginata were capable of a limited degree of thermoregulation. Operative temperatures and thermal quality (d_e=|T_set-min−T_e| and |T_e−T_set-max|) cycled daily with maximal thermal quality occurring during late morning and late afternoon. The accuracy of thermoregulation (d_b=|T_set-min−T_b| and |T_b−T_set-max|) was maximal (d_b values were minimal) as T_b declined and traversed T_set during the late afternoon–early evening hours and was higher on cloudy days than on sunny days because relatively low T_e values decreased the number of T_b values that were above T_set. Our index of thermal exploitation (E_x=frequency of T_b observations within T_set) was 36%, slightly lower than that reported for an Ontario population of C. picta marginata. Regression of d_b (thermal accuracy) on d_e (thermal quality) indicated that turtles invested more in thermoregulation when thermal quality was low and when water levels were high than when they were low. There were no intersexual differences in mean T_b throughout the year but females had relatively high laboratory determined T_b values in the fall, perhaps reflecting the importance of maintaining ovarian development prior to winter.     

Standard operative temperatures and cost of thermoregulation in the arctic ground squirrel,Spermophilus undulatus

Summary Body temperatures (T _b) and daily activity patterns of free-living arctic ground squirrells (Spermophilus undulatus) were determined via telemetry at a field site in northern Alaska. Simultaneous measurements were made of ambient temperature (T _a), wind speed (V), and incident solar radiation. The operative environmental temperature (T _e) for ground squirrels was obtained from fur-covered, thin metal taxidermic models of the animals. Standard operative temperature (T _es), a comparative index of heat flow, was calculated from T _e, V, and laboratory measurements of thermal conductivity.During the period of the study (August), S. undulatus were active for about 14 h per day (06.00 to 20.00 h). T _b was high throughout the daily cycle, averaging 38–39°C. Circadian variations in T _b were slight; average T _b values dropped <1°C at night. Daytime T _b fluctuations were not closely correlated to activity or to changes in environmental conditions. Air temperatures during the study were low, usually between 10 and 15°C during the day. However, T _es in exposed areas was normally higher, even though skies were generally overcast. During periods of sunshine, T _es may be as high as 34°C. The absence of nocturnal activity may result from increased costs of thermoregulation at night, which sharply reduces foraging efficiency. The high and stable body temperatures of S. undulatus probably result from thermoneutral daytime T _es, low activity levels, and the use of well-insulated nests.